TiN/Al alloy interfaces occur in the manufacture of semiconductor devices, where TiN may typically be used as a barrier layer to prevent the migration of Al into an adjacent layer. Such interfaces tend to break down at the high temperatures to which semiconductors are subjected and some means of stabilizing the interface is essential. It is known that oxygen can be used to stabilize the interface.
One technique used for the oxidation of the TiN surface prior to the deposition of an Al alloy is the air break technique (with or without a furnace anneal): This technique involves coating a cassette of wafers with TiN in a vacuum processing apparatus, venting the cassette of TiN coated wafers to air, loading the TiN coated wafers from ambient air to an "ex-situ" furnace (optional), annealing the TiN coated wafers in N.sub.2 at atmospheric pressure and at about 425.degree. C. for about 30 minutes (the N.sub.2 typically carries about 1 ppm of O.sub.2 impurity representing a partial pressure of about 7.6.times.10.sup.-3 Torr of O.sub.2) (optional), unloading the oxidized TiN coated wafers in ambient air (O.sub.2 partial pressure of 150 Torr) (optional), reloading the oxidized TiN coated wafers in the Al alloy deposition equipment, and degassing the oxidized TiN coated wafers at about 450.degree. C. for about 60 seconds.
In this particular case, the oxidation of the TiN layer occurs mainly during the air exposure (150 Torr O.sub.2 at 25.degree. C. for a duration of 60 minutes); the ambient air loading of the wafers into the furnace (150 Torr O.sub.2 from 25.degree. C. to 425.degree. C. for a duration of about 5 minutes); the N.sub.2 anneal into the furnace (7.6E-3 Torr O.sub.2 at 425.degree. C. and for a duration of about 30 minutes); and the ambient air unloading of the wafers (150 Torr O.sub.2 from 425.degree. C. to 25.degree. C. and for a duration of about 15 minutes).
Many manufacturers of integrated circuits use this air break technique and a furnace anneal. This technique cannot provide the high throughput and low cost process required for TiN and Al alloy depositions in commercial devices.
The oxidation can also be performed by exposing (one by one and for about 60 seconds) the TiN coated wafers to an "ex-situ" Rapid Thermal Processor (RTP) at atmospheric pressure at about 550 to 750.degree. C. in N.sub.2 (with typically 1 ppm of O.sub.2), NH.sub.3 (with typically 1 ppm of O.sub.2) or mixtures of one of these gases with some O.sub.2 before reloading the wafers in the Al deposition equipment. In this particular case, the oxidation of the TiN layer mainly occurs during the anneal into the RTP furnace (7.6.times.10.sup.-3 Torr O.sub.2 at 550 to 750.degree. C. and for a duration of about 60 seconds); and the ambient air cooling of the wafers (150 Torr O.sub.2 from 400.degree. C. to 25.degree. C. and for a duration of about 60 seconds).
While many manufacturers use this air break and RTP anneal technique in a production setting, it cannot provide the high throughput and low cost process required for the integration of TiN and Al alloy depositions.
The oxidation can also be performed by exposing (one by one and for about 60 seconds) the TiN coated wafers to an integrated RTP providing an "in-situ" oxidation of the TiN layer at about 550 to 750.degree. C. using about 5 to 20 mTorr of O.sub.2. The use of an integrated RTP module allows the high throughput and low cost process by integrating the deposition of TiN, the oxidation of TiN and the deposition of Al alloys in a single pump-down of a cluster tool. This technique has nevertheless two drawbacks. Firstly, when used at the high end of the temperature range, for example between 650 and 750.degree. C., TiSi.sub.2 is formed at the bottom of the contact by consumption of a thick layer of substrate Si. This situation is not very desirable for advanced semiconductor devices which use shallow junctions into substrate Si. Secondly, when used in the low end of the temperature range, for example between 550 and 650.degree. C., TiSi is formed and a smaller amount of Si is consumed, thus removing the first limitation. These temperatures are still high enough to cause a very thick oxidation (consumption) of the TiN layer within this 60 seconds duration. In other words, the low temperature RTP oxidation process allows too deep an oxygen penetration into the TiN layer.
It has been shown that the deeper the oxidation of the TiN layer, the deeper the penetration of the Al into the oxidized TiN during post Al deposition heat treatments. In order to prevent the complete oxidation (consumption) of the TiN layer, a very thick layer of TiN is required at the bottom of deep and small diameter contact holes. This requirement is very difficult to achieve, if not impossible, for contact holes of ever decreasing diameters.
The oxidation could also be performed by exposing (one by one and for about 60 seconds) the TiN layer to an "in-" O.sub.2 plasma at low temperature (for example, less than 450.degree. C.) prior to the deposition of Al alloys. The low temperature oxidation associated with O.sub.2 plasma would give a thin oxidation of TiN layers and would permit shallower TiN layers at the bottom of these small diameter contact holes. The use of an integrated O.sub.2 plasma would also provide the high throughput and low cost process by integrating the deposition of TiN, the oxidation of TiN and the deposition of Al alloys in a single pump-down of a cluster tool.
The above technique has two major drawbacks. Firstly, there would be serious hazard problems associated with pure O.sub.2 plasmas. Pure O.sub.2 plasmas result in the formation of large quantity of ozone, O.sub.3, a toxic gas. The pumping of large quantity of ozone with cryopumps results in the liquefaction of ozone which can suddenly explode when the toxic liquid drops onto warmer walls of the cryopump. The pumping of oxygen in large quantity results in a big block of frozen oxygen into the cryopump which may result in a very dangerous explosive gas mixture during power failures. The pumping of oxygen in large quantity results in critical regeneration of the cryopumps and special safety devices are required to prevent fire and explosions. Ion gauges are sources of ignition and explosion in pure O.sub.2 gases. Secondly, the pumping of pure O.sub.2 gas, from about 5 mTorr of O.sub.2 to a partial pressure of about 5.times.10.sup.-8 Torr of O.sub.2, is required after the completion of the plasma treatment and before the opening of the isolation gate valve of the process module to the wafer transfer module. The duration of this pump-down to a low enough O.sub.2 partial pressure would be too long and would be a throughput limiter for the cluster tool.
An object of the invention is to alleviate the aforementioned problems of the prior art.